PSI - Issue 61

Ilias Gavriilidis et al. / Procedia Structural Integrity 61 (2024) 315–321

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Gavriilidis et al. / Structural Integrity Procedia 00 (2024) 000–000

Fig. 1: Experimental curve of the X60 steel plate, and the corresponding numerical fit.

Table 1: Numerically predicted and measured inner diameter of the line pipe at JCO stage and JCO-E stage; the measurements have been obtained at 0, 45 and 90-degree locations from the weld seam.

JCOpipe

JCO-Epipe

Inner diameter (mm) Numerical simulation Actual (pipe mill)

0 ◦

45 ◦ 675

90 ◦ 679

0 ◦

45 ◦ 686

90 ◦ 686

675

687

675-677

678-681

683-689

684-686

686-687

686-688

outwards. The fabrication process ends with the removal of the expander segments and the final configuration of the pipe is referred to as “JCO-E pipe” (stage “iii” in Fig. 2c), which is the final product of the manufacturing process. The amount of expansion in the hoop direction of the pipe circumference is also called “expansion hoop strain” ( ε E = ( C E − C W ) / C W ) and expresses the di ff erence between the mid-surface lengths of the pipe circumference at the end of the expansion phase (stage “iii” in Fig. 2c), and at the JCO phase (stage “i” Fig. 2c). The value of expansion strain applied on the JCO pipe (stage “ii” of Fig. 2c) is equal to 1 . 3%, which is approximately the actual expansion strain considered in the pipe mill for the 30-inch-diameter pipe. The geometric characteristics of the JCO pipe and the JCO-E pipe are summarized in Table 1, in terms of inner diameter values at 0, 45 and 90-degrees position around the circumference. These numerical predictions are also in good agreement with actual measurements performed in the pipemill. An important forming parameter in JCO-E pipes with immense influence on the collapse capacity and the final geometry is the expansion strain ( ε E ). Fig. 3a presents the e ff ect of di ff erent expansion levels ( ε E ) on the collapse pressure ( P co ) of the JCO-E pipe. The collapse pressure is normalized by the yield pressure ( P y = 2 σ y t / D ), using the nominal geometric and material properties of the pipe ( D = 30 in, t = 1 . 523 in and σ y = 60 ksi). The results show that the collapse pressure increases with increasing expansion strain, up to a level of 0 . 7% approximately. From 0 . 7% to1 . 8% of expansion strain, the collapse pressure remains almost constant, while a maximum collapse pressure equal to 37 . 7 MPa is obtained at 1 . 8%. Beyond that point, the collapse pressure drops significantly, due to Bauschinger e ff ect which reduces the circumferential compressive yield strength upon reverse loading. It should be also noted that the maximum allowable expansion strain, according to DNV-ST-F101 standard (Det Norske Veritas, 2021), is 3.2. Influence of di ff erent expansion levels